/* 
背景        background
背景色      background-color
背景图片    background-image
背景重复    background-repeat
背景位置    background-position

背景大小    background-size  cover contain 100%
*/
.box{
    width: 300px;
    height: 300px;
    background: url(https://n.sinaimg.cn/news/transform/350/w210h140/20210712/2b50-29835ce2f8c08730d29607521b86ec43.jpg) no-repeat red;
    background-size: 100%;
}